In the running of heavy vehicles, e.g. trucks, buses and the like, vehicle economics have over time increasingly affected the profitability of the activity in which the vehicle is used. As well as the vehicle's procurement costs, the main items of expenditure involved in routine operation comprise driver pay, repair and maintenance costs and fuel to power the vehicle. It is therefore important to keep the costs involved in each of these areas as low as possible.
Depending on the type of vehicle, the significance of different factors may vary but fuel consumption is generally a major item of expenditure. The capacity utilisation of heavy vehicles is often high, resulting in high overall fuel consumption, so any means of reducing fuel consumption is likely to have positive effects on profitability.
Heavy vehicles in general have many different power train configurations, but since it is often desirable for vehicle running to be as comfortable as possible for the driver, automatically operated gearboxes are often used whereby decisions about gear changes and their actual implementation can be controlled by means of an on-board control system.
The fact that automatic gear changing in heavy vehicles is thus usually controlled by a control system makes it possible, is often utilised, to employ a mode of control whereby engine and gearbox control are partly based on commands from the vehicle's driver but wherein control and, for example, gear choice are also largely governed by the control system. For this reason, functions are often incorporated in the control system for improving fuel consumption by wherever possible running the vehicle as fuel economically as possible. These functions may for example take the form of functions for effecting gear changes and gear choice.
Another example of such a function is one whereby on downgrades the vehicle's engine is disconnected from its tractive wheels when the need to provide torque for maintaining the vehicle's speed is reduced. The vehicle's power train is closed again subsequently, e.g. when the driver presses an accelerator pedal or brake pedal.